1. Field of the Invention
The present invention relates to a transmission and reception system of transmission lines, and more particularly, to a transmitter, a receiver and an interface system capable of selective adoption of a differential current driving scheme and a differential voltage driving scheme.
2. Description of the Related Art
In the conventional art, in order to transmit and receive data at a high speed, a differential current driving scheme in which currents of different magnitudes are transmitted through a pair of transmission lines and data is restored using a current difference between the two transmission lines has been mainly used.
In the differential current driving scheme, a transmitter generates currents of different magnitudes which correspond to data to be transmitted and transmits the currents through two transmission lines, and a receiver restores the data using a current difference between the currents flowing through the two transmission lines. In the differential current driving scheme, when compared to a single current driving scheme, while the distortion of transmitted signals by noise is not substantial, interference occurs between the transmission lines due to the physical positions of the two transmission lines and the parasitic resistance, parasitic inductance and parasitic capacitance of the two transmission lines.
Although two differential currents flowing from the transmitter to the receiver are based on the assumption that two current sources used for generating the two differential currents source or sink the same current value, in practice, different current values can result due to process deviations. Also, when the currents which are sourced or sunk by current sources disposed in the receiver are distorted by the noise introduced through the transmission lines, the qualities of differential current signals are degraded.
Summarizing this, the transmitted signals are likely to be distorted due to interference between the two transmission lines, and the time constants of the transmission lines increase to lengthen the transition times of the signals, whereby the transmission speeds of the signals cannot but deteriorate.
FIG. 1 is a view showing signals of a true line, which are outputted from a transmitter of a conventional differential current driving system.
Referring to FIG. 1, when the current sources for generating the two differential currents produce current values of different magnitudes due to the above-described reasons, it is to be appreciated that the magnitudes shift by a preset deviation a, that is, an offset, each time when the direction of the current applied to the true line is changed.
The conventional differential current driving scheme and the system for realizing the scheme are unstable because they have the above-described problems. Therefore, novel data transmission and reception methods free from these problems are keenly demanded in the art.
While research has actively been made for a transmitter, a receiver and an interface system using the transmitter and the receiver to solve the above-described problems, in the case of the conventional differential current driving scheme, since data is transmitted using a limited current source, if the loads of the transmission lines are substantial, distortion of signals is likely to occur.